SIP is a network resource abstraction that obtains services. According to IETF RFC 3261, “SIP an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. These sessions include Internet telephone calls, multimedia distribution, and multimedia conferences.” SIP is a protocol developed by the IETF MMUSIC Working Group. SIP has been accepted as a 3rd Generation Partnership Project (3GPP) signaling protocol, as well as a permanent element of the IP Multimedia Subsystem (IMS) architecture. It is one of the leading signaling protocols for Voice-over-Internet Protocol (VoIP), along with H.323.
In IMS, SIP servers or proxies, collectively called Call Session Control Function (CSCF), typically provide centralized route engine, policy management, and policy enforcement point facilitating the delivery of multiple real-time applications using IP transport. This function is application-aware and uses dynamic session information to manage network resources (feature servers, media gateways, and edge device), and provides advance allocation of these resources per application and user context.
The Proxy-Call Session Control Function (P-CSCF) is a subscriber's first contact point within IMS; it may be from a visited network when roaming. It accepts requests and serves them internally or forwards them, e.g. to an Interrogating CSCF (I-CSCF) in the user's home network. The Serving-CSCF (S-CSCF) identifies the user's service privileges with the Home Subscriber Server (HSS), then selects and provides access to desired network facilities or resources. It is usually located in subscriber's home network. The Home Subscriber Server (HSS) is the master user database that supports IMS network entities that are handling calls/sessions. It contains subscription-related information, such as user profiles, performs authentication and authorization of a user, and provides physical information about the location of the user. The Interrogating-CSCF (I-CSCF) may be used by the P-CSCF to gain access to the right S-CSCF in the user's home network. In one example, the flow is P-CSCF to I-CSCF to S-CFCF to another network to I-CSCF to the HSS. In another example, the other (home) network's HSS may pass some amount of info to the current network's HSS thus avoiding the need to dial back to the home network for the info while roaming.
IMS is a standardized Next Generation Networking (NGN) architecture for telecommunications operators to provide fixed and mobile multimedia services. It uses a VoIP implementation based on a 3GPP-standardized implementation of SIP, and runs over the standardized IP. Existing packet-switched and circuit-switched telephone systems are supported. IMS provides all existing and new services that the Internet provides. IMS uses open standard IP protocols, as defined by the Internet Engineering Task Force (IETF). Thus, multimedia sessions between two IMS users, between an IMS user and a user on the Internet, or between two users on the Internet are established using exactly the same protocol. The interfaces for service developers are also based on IP protocols. IMS uses fixed wireline access (e.g., Digital Subscriber Loop (DSL), cable modems, Ethernet, etc.), mobile wireless access (e.g., Wideband Code Division Multiple Access (W-CDMA), Code Division Multiple Access 2000 (CDMA2000), Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), etc.), and fixed wireless access (e.g., wireless local area network (WLAN), Worldwide Interoperability for Microwave Access (WiMAX), etc.) to provide physical connectivity and Internet routing and applications technologies in order to provide services. Services with SIP are being integrated through the IMS architecture into a next-generation network (NGN) network.
Currently, user identification and authentication functionalities, including authorization and accounting, are done in a centralized location in IMS and other SIP-based systems. The main SIP network elements used for authentication and identification are the User Equipment (UE), P-CSCF, S-CSCF, and the HSS. The 3GPP Technical Specification 33.203 v7.3.0 (2006-09), which is herein incorporated by reference in its entirety, describes the current standard view of the interaction between these elements in identifying, authenticating, and registering users. Advantageously, centralized user identification and authentication alleviates the need for different applications to manage these functions. Further, new applications can be added without the need for separate identification and authentication interfaces.
Cisco Systems of San Jose, Calif. provides a CSCP Subscriber Database which uses a distributed data management model (details available at http://www.cisco.com/application/pdf/en/us/guest/products/ps6562/c1650/cdccont—0900a ecd80396990.pdf). However, the CSCP Subscriber Database is an alternative to the HSS. Further, the CSCP Subscriber Database distributes subscriber information to a Data Authority Server (DAS) which manages all profile and network data within an individual site or point-of-presence (POP), and not to network elements directly. Here, the network elements responsible for call session control, e.g., Cisco CSCP-SE (Service Engine), CSCP-EP (Edge Proxy), and CSCP-NRS (Name Resolution Server), interface to the DAS for authentication and identification. Disadvantageously, these methods introduce additional elements into the network, and replace the HSS in the IMS framework.
IMS and other SIP based systems are an architecture that relies on devices registering and on SIP to request services between user terminals. As described above, SIP can be used to request any service, such as Internet telephone calls, multimedia distribution, and multimedia conferences. For example, the requests can be for a video channel or video-on-demand (VoD). Currently, no mechanisms exist to cache resources requested by SIP like what is done at the HyperText Markup Language (HTML) layer. This is similar to the limitations in system architecture from the earliest stages of the World Wide Web (WWW) development with the Hyper Text Transfer Protocol (HTTP) and HTML.
Disadvantageously, IMS and other SIP based systems face performance issues as they scale due to the centralized authentication/identification, authorization and account, and with the consequent inherent lack of caching mechanisms for these key resources.